1. Field of the Invention
The present invention relates to a method of manufacturing a film structure in which a film made of a single crystal of potassium lithium niobate or a film made of a single crystal of potassium lithium niobate-potassium lithium tantalate solid solution is formed on a surface of a substrate made of a single crystal of potassium lithium niobate-potassium lithium tantalate solid solution, and also relates to a method of manufacturing an optical waveguide substrate and a second harmonic generation device utilizing the above manufacturing method.
2. Description of Related Art
A single crystal of potassium lithium niobate and a single crystal of potassium lithium niobate-potassium lithium tantalate solid solution have attracted much attention as a single crystal for a second harmonic generation (SHG) device generating a blue light used for a semiconductor laser. The single crystal mentioned above can convert to an ultraviolet ray having a wavelength of 390 nm. Therefore, by utilizing such a short wave light, the single crystal mentioned above can be applied in various fields such as optical disc memory, DVD laser light source, laser pointer, medical science, photo-chemistry, various kinds of light measurements. In addition, since the single crystal mentioned above has a large electro-optics effect, it can be applied for an optical memory device and so on utilizing its photorefractive effect.
In an optical application, particularly, a second harmonic generation application, it is necessary to transmit a short wavelength laser light having a wavelength of for example 400 nm in the single crystal with a large output density as large as possible. In addition, it is also necessary to suppress a optical damage as small as possible. In this manner, a optical damage must be suppressed, but for this purpose it is necessary to use a single crystal having excellent crystallinity that constitutes the optical waveguide. Moreover, it is necessary to use the optical waveguide having a single domain structure. Therefore, from a practical viewpoint, the single crystal mentioned above is required to generate a second harmonic wave having a high output such as for example 30 mW.
In Japanese Patent Laid-Open Publication No. 8-6083 (JP-A-8-6083), an epitaxial clad layer made of a single crystal of potassium lithium niobate-potassium lithium tantalate solid solution is arranged on a surface of a substrate made of a single crystal of potassium lithium niobate, and an optical waveguide made of the solid solution single crystal mentioned above is formed on the clad layer by a metalorganic chemical vapor deposition method. However, in this device, a optical damage still remains, and a second harmonic output does not reach to a high level mentioned above.
In Jpn. J. Appl. Phys. Vol. 37 (1988) pp. 5582-5587, a potassium lithium niobate film is formed on a (111) Si substrate by a metalorganic chemical vapor deposition method. However, since a crystal structure of potassium lithium niobate is remarkably different from a crystal structure of (111) Si, a polycrystal film is formed.
An object of the invention is to generate a film having excellent crystallinity made of a single crystal of potassium lithium niobate or a film made of a single crystal of potassium lithium niobate-potassium lithium tantalate solid solution on a substrate made of a single crystal of potassium lithium niobate-potassium lithium tantalate solid solution.
Moreover, an another object of the invention is to provide an optical waveguide having a small optical damage and to increase largely a second harmonic generation output.
According to the invention, a method of manufacturing a film structure in which a film is formed on a surface of a substrate, comprises the steps of: preparing a substrate made of a single crystal of potassium lithium niobate-potassium lithium tantalate solid solution; and forming a film made of a single crystal of potassium lithium niobate or a film made of a single crystal of potassium lithium niobate-potassium lithium tantalate solid solution on a surface of the substrate under such a condition that a temperature of the substrate is maintained in a range of 700xc2x0 C.-850xc2x0 C. and the film is formed by a metalorganic chemical vapor deposition method.
Moreover, according to the invention, a method of manufacturing an optical waveguide substrate in which an optical waveguide is formed on a surface of the substrate, comprising the steps of: preparing a substrate made of a single crystal of potassium lithium niobate-potassium lithium tantalate solid solution; and forming a film made of a single crystal of potassium lithium niobate or a film made of a single crystal of potassium lithium niobate-potassium lithium tantalate solid solution on a surface of the substrate under such a condition that a temperature of the substrate is maintained in a range of 700xc2x0 C.-850xc2x0 C. and the film is formed by a metalorganic chemical vapor deposition method so as to form the optical waveguide.
Further, according to the invention, a method of manufacturing a second harmonic generation device in which an optical waveguide for exchanging a fundamental wave to a second harmonic wave, comprising the steps of: preparing a substrate made of a single crystal of potassium lithium niobate-potassium lithium tantalate solid solution; and forming a film made of a single crystal of potassium lithium niobate or a film made of a single crystal of potassium lithium niobate-potassium lithium tantalate solid solution on a surface of the substrate under such a condition that a temperature of the substrate is maintained in a range of 700xc2x0 C.-850xc2x0 C. and the film is formed by a metalorganic chemical vapor deposition method so as to form the optical waveguide.